Standard Operating Procedure II: EDS (Bruker Flat-Quad)

Transcription

1 Standard Operating Procedure II: EDS (Bruker Flat-Quad) ywcmatsci.yale.edu ESC II, Room A119F 810 West Campus Drive West Haven, CT Version 1.1, October 2018

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3 > FOLLOW the SOP strictly to keep the instrument in good condition. Any violation will lead to user account suspension. > NEVER use your own USB drive on instrument computer. Data can be transferred with the Jump Drive provided by the Core. > NEVER surf the web on the instrument computer to minimize the risk of the computer being hacked. > NEVER allow other users to get access to instrument computer on your reservation. > REPORT any issues to Core director immediately so they can be fixed on time. 1

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5 Table of Contents 1 Introduction Sample Preparation Starting Instrument System Status Check EDS Sample loading EDS setup on computer EDS setup on EDS computer EDS measurement Closing EDS detection:

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7 Energy Dispersive Spectroscopy (EDS) Standard Operating Procedure 1 Introduction 1) Instrument features: > Cold field emission (CFE) e-beam source: high resolution on conductive surfaces (0.8 nm on Au clusters/magnetic tape) > Sliding-in annular Energy Dispersive Spectroscopy (EDS) detector: high elemental mapping resolution > Sliding-in annular Photo Diode PD-BSE detector: high signal intensity from backscattered electron > Scanning Transmission Electron Microscopy (STEM) detector: high resolution compositional contrast imaging, ideal for EDS mapping 2) Location Materials Characterization Core Room E West Campus Drive West Haven, CT ) Primary Staff Contact Dr. Min Li Tel: min.li@yale.edu Office: ESC II, Room E119D Zishan Wu, Lab Assistant zishan.wu@yale.edu (cell) Office: ESC II Yiren Zhong, Lab Assistant yiren.zhong@yale.edu (cell) The Yale West Campus MCC Facilities are operated for the benefit of all researchers. If you encounter any problems with this facility, please contact the staff member listed above immediately. There is never a penalty for asking questions. If the equipment is not behaving exactly the way it should, contact a staff member. Warning: Please follow strictly the SOP to keep the facility at good condition. We DO NOT recommend user explorations on program unless endorsed by core director. 1

8 2 Sample Preparation 1 Note: TEM samples can also be used with a dedicated TEM sample holder for EDS. The EDS mapping resolution can reach below 100 nm with TEM samples using STEM-EDS mode. 1) Always wear gloves for vacuum sample preparation! Change gloves if touched computer keyboard and mouse. 2) Follow instructions from SOP to prepare samples. 3) Align sample surface strictly with the height gauge tip as shown below. Warning: Samples mounted above Height Gauge tip will hit the EDS detector and the repair fee ($40,000) will be charged to PI s account. Note: no need to use height gauge if TEM sample holder is used. 4) Clean sample holder: bring the specimen stub inside the fume hood and blow off loose particles on the sample surface using the N2 gun. 2 3 Starting Instrument Follow Section 3 Starting Instrument in the separate SOP. 4 System Status Check Follow Section 4 System Status Check in the separate SOP. 5 EDS Sample loading 1) Follow Section 5 Loading the Specimen in the separate SOP and leave the sample at exchange position 2) Turn off the small LCD from the back (top left) to avoid EDS detector damage and EDS spectra distortion. Warning: The LCD unit also provides power to the infrared camera inside main chamber. If it is left on during /EDS scan, the camera will continuously emit infrared light to flood the EDS detector even at fully extracted position and shorten its lifetime quickly. 6 EDS setup on computer 1) In PC_ program on the computer (left side), click HOME button to move the sample holder to HOME position 2) Turn off the small LCD by pressing the switch in the back top-left corner of the monitor. 1 Always wear gloves for your sample preparation in your own lab or in MCC! Warnings will be given for violations and the user account will be revoked after three warnings with notice to PI. Further training at PI s expense will be required to resume the account. 2 This step is crucial to keep the chamber vacuum at good pressure, which in turn improves the imaging resolution with less surface contamination and keeps the lens system at good condition. 2

9 Note: This step is crucial, otherwise the EDS detector will be flooded by ambient signals leading to fat peaks in spectra. 3) Click Set button in the Stage tab in the popup window below: 4) Check the FQ-EDX box in the popup window below and hit OK. 5) The stage Z position should move to the default height at 14 mm.as highlighted in the window below: Warning: Never change the Z position < 11 mm. This will cause the sample holder crashing into the EDS detector. This severe SOP violation will lead to user account suspension and charge on PI s account. 6) Check the working distance (W.D.) in PC_ below and make sure it is set at 15 mm. If not, click on the top menu bar to switch imaging mode from LM (low magnification) to high magnification, then change W.D. in the window below. Switch back to LM. 7) Make sure Vacc (e-beam accelerating voltage) is OFF (check in PC_ program) 3

10 Note: it is OK to leave the e-beam ON if decide to do EDS in the middle of measurements. 8) E-beam parameter setup for EDS: a) E-beam voltage (the overvoltage to excite EDS X-ray emission lines) setup: > Check the EDS periodic table and choose a set of characteristic X-ray emission lines for intended sample elements that have least energy overlapping. > The chosen e-beam voltage, the overvoltage should be at least 1.5x the highest X- ray line in matrix elements and below 20 kv. Tip: smaller beam voltage means higher EDS special/mapping resolution. Warning: NEVER choose e-beam voltage above 20 kev!! The EDS detector will be burned!! The user s EDS access will be suspended and the cost ($70k) will be charged on PI s account. b) E-beam current setup: > Switch to High Magnification (HM) mode, set the Probe current to High in the Operation condition window below. > For chosen overvoltage smaller than 12 kv, consider increasing the e-beam current further by lowering the Cond. Lens1 in the window below: select smaller numbers than default EDS setup on EDS computer 1) Log into EDS computer through FOM Screen Locker. a) The EDS software Esprit window should be always kept ON. b) If the Esprit program was closed and the EDS computer was logged off, select the profile PC- with password hitachi 2) Check EDS detector window position on the detector highlighted on the pictures below and make sure it was set by previous user at 20 kv. If not, report to manager immediately. Warning: It is the serious SOP violation if forgot to switch the detector window back to 20 kv after use. This may lead to detector damage and repair charge will be applied to user s PI account. 4

11 20 kv 3) Check to make sure the Specimen Chamber SC pressure is at LE-4 Pascal. 4) Switch EDS detector in operation mode and set up detector configuration parameters: a) In EDS Esprit operating program, click the triangle in the EDS tab at the bottom left corner as indicated below: b) In the EDS DETECTOR CONFIGURATION popup window below: > Check 130 kcps in Pulse throughput and 20 kev in Maximum energy. > Make sure the Thermostat is checked in Cooling setting. > Check Normal operation in Mode setting. Select Yes in the popup INFORMATION window. Warning: the EDS detector cooling should be started only when the Specimen Chamber pressure has reached LE-4 Pascal to minimize detector contamination. 5

12 c) Close both INFORMATION and EDS DETECTOR CONFIGURATION window above. d) The EDS detector will be cooled to the operating temperature of -20 ± 0.5 ºC in about 5 minutes. 5) EDS detector window setting at different overvoltage/e-beam voltage: a) If the beam voltage 6 kv: > Enter Esprit System window by clicking button on the bottom left of the side menu and clicking tab as shown below. Click button to open Detector Data window and select 1µm Mylar from dropdown list. > Go back to EDS detector head on chamber, switch the detector window from 20 kv to 6 kv. 6

13 b) If the beam voltage is between 6 kv and 12 kv: > Enter Esprit System window by clicking button on the left side menu and clicking as shown below. Click to open Detector Data window and select 1+2 µm Mylar from dropdown list. > Go back to EDS detector head on chamber, switch the detector window from 20 kv to 12 kv. c) If the beam voltage is larger than 12 kv (Never change voltage to above 20 kv to damage the detector): > Enter Esprit System window by clicking button on the left side menu and clicking as shown below. Click to open Detector Data window and select 1+6 µm Mylar from dropdown list. > Go back to EDS detector head on chamber, switch the detector window from 20 kv to 20 kv. 8 EDS measurement 1) During EDS detector cooling, turn on e-beam in PC_ program and find the area of interest. 2) Check EDS detector and make sure it has reached the operation temperature -20 ± 0.5 ºC 3) Click button in EDS tab in Esprit program and click OK on DETECTOR POSITION window to move the detector to the acquisition position right above sample. Warning: > If users decide to run EDS in the middle of imaging, make sure to check FQ-EDS mode in PC_ program Stage > Set setting window to bring down the sample stage to required EDS stage height (14 mm). Please check Section 6, Step 3) on page 3. 7

14 > Failure to follow will lead to EDS detector crashing into sample stage. User s access will be suspended and repair cost will be charged on PI s account. 4) EDS dead time adjustment (check steps in Spectrum Acquisition mode below): > As shown in the EDS tab below, the Dead time in percentage denotes the signal processing capability of the EDS controller. The higher number indicates the higher signal counts and the possibility of the signal pileup or false peak appearance. The Dead time should be kept around 30%. Tips: > To improve EDS mapping resolution, the dead time should be kept just above 10%. The input count rate (ICR) should be at least one hundred of kcps to keep a good signal/noise ratio. > For spectral acquisition, the dead time can be kept at around 30%. 5) Spectrum Acquisition Mode: Note: Make sure the imaging area for spectrum collection is homogeneous if using this mode. Consider Objects mode next for inhomogeneous surfaces. a) Go back to PC_ window, decide the image magnification and make an initial adjustment on focus and stigma to get a good image. b) In EDS Esprit window click on the left side menu to enter Spectra workspace c) Click button and check and adjust the Dead time within ~10 30%: > If the Dead time is below 10%, in PC_ window (do the opposite steps if Dead time is above 30%): > Increase the e-beam emission current (maximum 30 µa); > Choose High Probe current; > If necessary, change Cond. Lens 1 setting from 5 to 1 or 2, the smaller number the higher the signal intensity. 8

15 d) Leave spectral acquisition on, go back to PC_ window, adjust focus and stigma to get sharp image. e) If a good signal/noise ratio has achieved on the spectrum, click again to stop acquisition. f) To add collected spectrum into project or report, hit the button on the top right corner of the spectral workspace g) To save the data in Bruker spectra format (*.spx) or export to *.txt or *.xlsx format, click the lower button. 6) Objects Mode: Note: this mode should be chosen for inhomogeneous surface spectral analysis. a) Adjust Dead time within 10 30% in Spectrum Acquisition Mode above b) Hit on the left side menu to enter Object workspace c) In PC_ window adjust focus and stigma to get sharp image d) Go back to EDS Esprit window and click button to capture image. e) Select the desired object type on the bottom menu bar and click on captured image above to specify positions. Tips: > The EDS spatial resolution is e-beam voltage/overvoltage dependent which is around 1 µm. > Choose Point object mode if the interested feature is too small. > Allow longer collection time if the point or small square or circle objects are chosen. f) Click to highlight all objects and click g) If a good signal/noise ratio has achieved on the spectrum, click again to stop acquisition. h) To save object data, click the button on the top right corner of the workspace window. i) To save the spectrum, click the lower spectrum chart. 7) Line Scan Mode: a) Adjust Dead time within ~ 10 30% in Spectrum Acquisition Mode 9

16 b) Hit on the left side menu to enter Line Scan workspace c) In PC_ window adjust focus and stigma to get sharp image d) Go back to EDS Esprit window and click button to capture image. e) Highlight the line and drag and adjust the endpoints to the desired position f) Set Point count of the line scan and click g) Use the icon to identify elements h) If a good signal/noise ratio has achieved on the spectrum, click again to stop acquisition. i) To save line scan data, click the button on the top right corner of the workspace window. j) To save the profile, click the lower profile chart. 8) Mapping Mode: a) Adjust Dead time to be just above 10 % in Spectrum Acquisition Mode b) Click button on Scan tab to activate image drift correction. Make sure the button is highlighted in red to enable drift correction. c) Hit on the left side menu to enter Mapping workspace d) In PC_ window adjust focus and stigma to get sharp image e) Go back to EDS Esprit window and hit button to capture image. f) Click button to start Mapping. g) Use the icon to identify elements in spectrum window during mapping. 10

17 h) Before stop mapping: > Click Spectrum tab above the top right corner of Map window, make sure a good signal/noise ratio on interested elemental peaks in the spectrum. > Check if the mapping resolution has not improved with time. Typical mapping collection time depends on signal intensity (~ mins or even longer). i) Click again to stop Mapping. j) To save map data, click the button on the top right corner of the workspace window. k) To save the map image, click the lower image window. l) To save individual element image in the thumbnail on the bottom, click the thumbnail bar. 9 Closing EDS detection: 1) In PC_ program, click the OFF button to turn off electron beam Note: the beam can be left ON if plan to do further imaging. 2) Click Standby button in EDS DETECTOR CONFIGURATION window to switch the EDS detector to Standby Mode 11

18 3) Check EDS detector window position and make sure it is switched back to 20 kv: Warning: It is crucial to set the detector window back to 20 kv to avoid e-beam damage. Violation will lead to detector damage and repair charge will be applied to user s PI account. 20 kv 4) Fully retract EDS detector by clicking in EDS Esprit program and wait until the detector is fully retracted. 5) In EDS Esprit window, go to tab, click button to open Detector Data window and select 1+µm Mylar from dropdown list. 6) In PC_ window: > Change Vacc back to 10 kv and the Ie back to 10 µa > Change the Probe current back to Norm. > Change the Cond. Lens1 back to 5.0 in the window below: > Click the EXC button to move the specimen stage to the exchange position. Note: click Home button if continue to do imaging. > Click Set button in the Stage tab; uncheck FG-EDX box below. 12

19 7) Wait for the EDS detector temperature rises above 20 C (~ 20 minutes, be patient!) and then take sample out of chamber. Warning: Never start sample transfer while EDS detector is still being cooled. This will induce contamination on the detector if still below 20 C when the Specimen Chamber door is open. 8) During EDS detector warmup: > Make sure sample holder is at exchange (EXC) position > Data transfer is complete > Log off FOM on computer in your FOM account. 9) Check to make sure the EDS detector temperature rises above 20 C and then 10) Turn ON small LCD 11) Finish sample unloading from chamber. 12) Turn OFF small LCD 13) Log off FOM on EDS computer Note: Keep Esprit program ON and maximized on screen 14) Clear the work bench and dispose gloves, Kimwipes 13

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